Tetrasomy 18p

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Description

Tetrasomy 18p, also known as 18p syndrome or trisomy 18p, is a rare genetic disorder characterized by the presence of an extra copy of the short arm (p arm) of chromosome 18. This extra genetic material leads to a variety of physical, developmental, and intellectual challenges. While tetrasomy 18p is uncommon, understanding its features, causes, and management is crucial for providing appropriate care and support to individuals and families affected by this condition.

Genes Involved

The short arm of chromosome 18 contains numerous genes, and the duplication of this region disrupts the normal balance of gene expression. Some of the genes involved in tetrasomy 18p include:

• RMRP: Associated with mitochondrial function and ribosome biogenesis
• SNORD115: A small nucleolar RNA gene involved in ribosome assembly
• MYH14: A gene involved in muscle development
• SNRPN: A gene associated with Prader-Willi syndrome, a distinct genetic disorder
• UBE3A: A gene related to Angelman syndrome, another distinct genetic disorder

The exact contribution of each gene to the specific features of tetrasomy 18p is still being investigated.

Recognizing the Signs and Symptoms

The signs and symptoms of tetrasomy 18p vary widely among individuals, but common features include:

• Physical characteristics:
  • Small stature
  • Microcephaly (small head size)
  • Characteristic facial features such as a prominent forehead, widely spaced eyes, and a small nose
  • Cleft lip or palate
  • Heart defects
  • Skeletal abnormalities
• Developmental delays:
  • Intellectual disability
  • Speech and language difficulties
  • Motor delays
  • Behavioral issues
• Other:
  • Seizures
  • Feeding difficulties
  • Vision and hearing problems

Causes

Tetrasomy 18p occurs due to a random event during the formation of eggs or sperm. It is not typically inherited from parents. The extra copy of chromosome 18p can occur in one of two ways:

• Trisomy 18p: An extra copy of the entire short arm of chromosome 18 is present in all cells.
• Mosaic tetrasomy 18p: The extra copy of chromosome 18p is present in some cells but not others.

Inheritance/recurrence risk

Tetrasomy 18p is not typically inherited, meaning it is not passed down from parents to their children. The recurrence risk is generally low, but it is slightly increased if there is a history of chromosomal abnormalities in the family. Genetic counseling can help assess the risk for future pregnancies.